I used my old Motopak GT-27 when I had the stock steel tank. It's big, 20L expandable to 27, but worked well. Magnetic so easy on/off. It's a little beat up looking as it survived me totaling my Vstrom but got smashed up some in the process. Doesn't account for the angle though either.
I got the a smaller strap type motopak for the XT225 plastic Clarke tank, but that does not strap well so looking at a Wolfman.

I got the a smaller strap type motopak for the XT225 plastic Clarke tank, but that does not strap well so looking at a Wolfman.